<template>
  <ul class="list">
    <li class="item"
    v-for="item of letters"
    :key="item"
    :ref='item'
    @touchstart.prevent='handleTouchStart'
    @touchmove='handleTouchMove'
    @touchend='handleTouchEnd'
    @click="handleLetterClick">
    {{item}}
    </li>
  </ul>
</template>

<script>
  export default{
    name:'CityAlphabet',
    props:{
      cities:Object
    },
    computed:{
      letters (){
        const letters = []
        for(let i in this.cities){
          letters.push(i)
        }
        return letters
      }
    },
    data () {
      return {
        touchStatus:false,
        startY:0,
        timer:null
      }
    },
    updated() {
      this.startY=this.$refs['A'][0].offsetTop
    },
    methods:{
      handleLetterClick(e){
        this.$emit('change',e.target.innerText)
      },
      handleTouchStart(){
        this.touchStatus=true
      },
      handleTouchMove(e){
        if(this.touchStatus){
          if(this.timer){
            clearTimeout(this.timer)
          }
          this.timer = setTimeout(() => {
             const touchY=e.touches[0].clientY-79
             const index= Math.floor((touchY-this.startY)/20)
              if(index >= 0 && index< this.letters.length){
                this.$emit('change',this.letters[index])
          }
          },16)
        }
      },
      handleTouchEnd(){
        this.touchStatus=false
      }
    }
  }
</script>
<style lang="stylus" scoped>
 @import '~styles/varibles.styl'
 .list
    display :flex
    flex-direction :column
    justify-content :center
    position :absolute
    top :1.58rem
    right :0
    bottom :0
    width :.4rem
    .item
      line-height :.4rem
      text-align :center
      color :$bgColor

</style>
